The present invention is related to the crystallization of protease enzyme at a temperature greater than 10.degree. C. More particularly, the present invention relates to selective crystallization of protease enzyme in an aqueous solution using sodium sulfate.
Intensive research efforts have been directed to the precipitation and crystallization of enzymes as a means of purification and preparation of enzyme products. For example, in U.S. Pat. No. 4,659,667, a process is disclosed for the recovery of an enzyme from solution by concentrating to supersaturation the enzyme-containing solution at pH near the isoelectric point of the enzyme, inducing crystallization and recovering the crystallized final product. Inducing crystallization is achieved by allowing the enzymes to spontaneously crystallize upon concentration or by seeding, sound, stirring or scratching the inner surface of the container. Crystallization of alpha-amylase is exemplified.
In PCT Publication No. WO 89/08703, a process is described for the crystallization of subtilisin by adding a halide salt, such as sodium chloride or calcium chloride, to a concentrated subtilisin solution of at least about 40 grams per liter.
In EP 506,866, a method for the crystallization of enzymes is disclosed which is characterized by using as a starting material an aqueous solution containing liquid with a relatively high enzyme purity and a concentration of enzyme of about at least 5 grams per liter and adding as a crystallization agent an easily soluble salt of the non-halide type to a concentration which is considerably smaller than the amount necessary to precipitate the enzymes in an amorphous form. Crystallization of certain subtilisin enzymes at temperatures up to 30.degree. C. is exemplified. Sodium sulfate is used to help purify the protease product but not for crystallization.
In spite of these advances in the field of enzyme crystallization, inexpensive and efficient crystallization of proteases suitable for large scale production has remained problematic in industry. The ability to use room temperature and an inexpensive salt for industrial scale crystallization of protease would represent a large savings and be of great importance to the industry.